ASNV Urges Stop Killing Caterpillars

ASNV and eleven other organizations are urging Fairfax County and Prince William County to end their insecticide spraying programs targeting the native fall cankerworm, an effort that ASNV undertook in 2013.

Beginning in 2000 and for several years since then, Fairfax County has conducted helicopter and truck spraying of an insecticide in the spring to control the caterpillar of a native insect called the "fall cankerworm" (Alsophila pometaria). The County sprays at a time when many species of birds are breeding, raising young and some birds, especially warblers, are migrating through Northern Virginia. Caterpillars are an important food source for many birds. The insecticide is potentially deadly not just to the targeted fall cankerworm, but to all exposed butterfly and moth caterpillars. These butterfly and moth species, like the fall cankerworm, provide food for birds, beetles, bats, frogs, spiders and other wildlife. And the insecticide, a commercial application of Bacillus thuringiensis subsp. kurstaki (Btk), can "drift" to other areas outside the spray areas.

The most recent fall cankerworm insecticide spraying took place in the spring of 2015, when the County sprayed insecticide by truck over 66 acres in neighborhoods in the Mt. Vernon and Mason Magisterial Districts of Fairfax County. One neighborhood targeted for spraying is adjacent to Columbia Elementary School which hosts a native plant garden.

In the spring of 2014, the County sprayed insecticide by helicopter and truck over approximately 2,000 acres in the Mount Vernon, Lee and Mason Magisterial Districts of Fairfax County, with more than 70% of the spray areas located in the Mount Vernon District.

The fall cankerworm, Alsophila pometaria, is a native moth of North America in the taxonomic order Lepidoptera that is in its caterpillar stage in the spring. The adult moths emerge from the ground in the autumn. The adult females, which do not have wings, climb trees to lay their eggs. On their way up the trees, the female moths mate with the males, which have wings and fly. The eggs hatch in the spring, and the hungry caterpillars find leaves to eat. After about a month of feeding, the caterpillars spin down on a silken thread on their way to other trees or to the ground, where they burrow underground to pupate and emerge as adults in the fall. It is called the “fall” cankerworm because of its adult status as a moth in fall. Cankerworm caterpillars are commonly referred to as “inchworms.”

The fall cankerworm is an important food source for birds and other wildlife. Fall cankerworm caterpillars are an ideal food source for birds because they are smooth, without hair or spines, and lack chemical defenses. The fall cankerworm does not pose a risk to human health or safety; it does not bite or sting, nor is it known to transmit human disease.

Despite its native status and ecological benefits, the fall cankerworm unfortunately is sometimes referred to as a “pest.” Some people are annoyed or distressed by the appearance of the fall cankerworm spinning down on a silken thread on its way to the ground. The caterpillars sometimes land on outdoor areas like patios and sidewalks. The fall cankerworm caterpillar is also described by some people as a “pest” because it munches on the leaves of deciduous trees and shrubs causing some leaf damage, which in extreme cases can injure trees (See “Does the fall cankerworm hurt or kill trees?” below) and which some people find unappealing.

When the hungry caterpillar emerges in springtime, it munches on the leaves of a variety of deciduous trees and shrubs, especially elm, ash and maple, and also hackberry, oak, various members of the rose family, walnut, and willow.*

Most trees quickly recover from the leaf damage, which is also referred to as defoliation. If the same tree is completely defoliated for three or more consecutive years, limb dieback or loss of vigor can result.** Other factors, such as a tree’s age, exposure to other stresses such as drought, and its vigor will cause a tree to be more susceptible to injury from defoliation.**

Fairfax County does not measure the effect of tree defoliation caused by the fall cankerworm on the health of trees and does not measure tree mortality. Tree defoliation surveys in 2015 showed approximately 0% of the tree canopy defoliated and the County estimates 1% defoliation of the tree canopy in 2016 and for 2017.***

A caterpillar is a butterfly or moth in an immature stage of life. All butterflies and moths, including the fall cankerworm, which is a moth, are members of the taxonomic order Lepidoptera and are insects.

Many caterpillars become butterflies, which many people find to be a source of beauty and inspiration. Insects play a central role in the ecosystem by being a food source for birds and other animals, pollinating plants and spreading seeds, improving soil fertility, and sustaining forest health and diversity.* Some insects kill weak trees which can benefit the overall health and resistance of the forest.* While 1% of the insects on earth interact with humans in negative ways, like mosquito bites, 99% of insects pollinate plants, return nutrients tied up in dead plants and animals to the soil and provide food, directly or indirectly, for most other animals.**

Bacillus thuringiensis (Bt) is a naturally occurring soil bacterium that produces poisons that cause disease in insects.* There are various subspecies of Bt, and these differ in their toxicity to insects. The Bt subspecies kurstaki (Btk) is deadly to immature butterflies and moths (caterpillars). Btk acts as a stomach poison that causes caterpillars to stop eating and to starve to death within about a week of ingestion. The insecticide sprayed by Fairfax County is a commercial application that includes ingredients in addition to Btk. (See “What is Foray 48B?” below.)

Foray 48B is the commercial application of Btk currently used by Fairfax County.* Foray 48B is comprised of Btk (13%) and “Other Ingredients” (87%) that are not publicly disclosed by the manufacturer.** For more information about the ingredients of Foray 48B, see “Does Btk affect humans?”.

According to the manufacturer’s label: “This product must not be applied aerially within 1/4 mile of any habitats of threatened or endangered Lepidoptera.”

This statement is an acknowledgement that the insecticide is potentially deadly to all butterfly and moth caterpillars and that caterpillars are at risk from “drift” of the insecticide.

As far as we know, Btk does not directly harm mammals, bees, fish, or insects other than butterfly and moth caterpillars.* Btk is potentially deadly to all butterfly and moth caterpillars that are out at the time of spraying or while the insecticide persists on leaves or needles. Butterflies and moths, in their multiple stages of life, are an important food source for birds, beetles, bats, frogs, spiders and other wildlife. It should be noted that if a butterfly or moth is killed in its caterpillar stage of life by the insecticide, it will not, for example, grow into an adult, thereby depriving moth or butterfly predators of a food source, and will not lay eggs, thereby depriving animals that feed on insect eggs of a food source. Adult moths are food for Eastern screech owls and other wildlife like the Eastern red bat, which is a moth specialist. By killing caterpillars, the insecticide indirectly harms birds and other animals and could reduce their populations. (See “Which birds could be harmed?” )

Btk is potentially deadly to all butterfly and moth caterpillars that are out at the time of spraying or while the insecticide persists on leaves or needles. A “caterpillar” is a butterfly or moth in an immature stage of life.

The Audubon Society of Northern Virginia’s Jim Waggener has led surveys of butterflies and other wildlife for several decades in the Lower Potomac area of Fairfax County. According to the past decade of data, 62 species of spring butterflies have been documented in Occoquan Regional Park and the Meadowood Special Recreation Management Area. Two of these butterflies include the Frosted Elfin, a Commonwealth Species of Greatest Conservation Need (http://bewildvirginia.org/species/ then click on “Terrestrial Insects”), and the Eastern Tiger Swallowtail, the state insect of Virginia. The spring butterflies are at greatest risk of being harmed by Fairfax County’s Btk spraying program because their caterpillar stage, when they are vulnerable to Btk, precedes their adult (butterfly) form. To see the complete list of spring and summer butterflies, click here.

If you are interested in joining Jim Waggener and other volunteers for a butterfly and dragonfly survey or a general wildlife survey, please click here.

Moth and butterfly species are an important food source for birds. By spraying an insecticide that kills moth and butterfly caterpillars, Fairfax County is depriving migrating and breeding birds of an important food source at a critical time. Migrating birds pass through the County hungry and tired in the spring at the same time that the fall cankerworm and other caterpillars emerge, an excellent example of nature’s synchronicity or phenology. These and other birds depend on, and time their migration to feed on, historically-reliable insect supplies along the East Coast en route to their breeding destinations in the northern U.S. and Canada.

In addition, breeding birds in the County rely heavily on insects for protein to produce and feed their chicks. For example, chickadees eat a diet comprised 80 – 90% of insects (such as caterpillars) and spiders in the spring,* and feed their young a diet that is more than half comprised of caterpillars alone.** Douglas Tallamy has observed Carolina chickadees, a common bird species in Fairfax County, feeding their offspring between 300 and 590 caterpillars a day.***

**Kluyver, H. N. 1961. “Food Consumption in Relation to Habitat in Breeding Chickadees,” The Auk, 78: 532-550. The Auk is published by the American Ornithologists’ Union. It should be noted that a bird’s prey base will vary depending upon weather and other factors. This article described Black-capped chickadees, a species closely related to the Carolina chickadee. Kluyver observed chickadees bringing to the nest in a single feeding session 65 food items, all animal food items and which included 35 caterpillars.

***http://blog.nwf.org/2013/05/help-bugs-and-birds-by-growing-native-plants/ (interview with Douglas W. Tallamy, professor and chair of Department of Entomology and Wildlife Ecology at University of Delaware).

Local bird expert, conservationist and Fairfax County resident Larry Cartwright has prepared lists of migrating and breeding birds of Northern Virginia that likely are indirectly harmed as a result of the County’s insecticide spraying program for the reason that caterpillars are a major food source for these birds. These lists show various declining or rare bird species that have been identified by the American Bird Conservancy and the U.S. Fish and Wildlife Service. Click here.

The insecticide sprayed by Fairfax County is potentially deadly to all butterflies and moths that are in their caterpillar stage at the time of spraying and to those caterpillars that emerge while the insecticide persists on leaves and needles. We have prepared a list of 110 forest caterpillars in the Eastern U.S. that are present in April and May. The list can be found here. (In 2014, for example, the insecticide was sprayed in Fairfax County on April 28 and May 1). Unfortunately, this list likely represents an undercount for the reason that although it is estimated that some 5,000 species of butterflies and moths are found east of the 100th meridian, our list is drawn from a list of only 245 species* (less than 5% of the estimated total) as only modest literature on caterpillar identification exists.**

(2) “Few studies have been conducted on the chronic health effects, carcinogenicity, or mutagenicity of B.t. People exposed to B.t. have complained of respiratory, eye, and skin irritation, and one corneal ulcer has occurred after direct contact with a B.t. formulation. People also suffer allergies to the “inert” (secret) ingredients. People with compromised immune systems may be particularly susceptible to B.t.”

Foray 48B, the commercial application of the insecticide used in Fairfax County, is comprised primarily of undisclosed ingredients, which are also referred to as “trade secret” or “inert” ingredients. (See “What is Foray 48B?” above). In the past, Foray 48B has been found to contain small amounts of lye (sodium hydroxide), sulfuric acid, phosphoric acid, methyl paraben, and potassium phosphate. See “Insecticide Fact Sheet: Bacillus Thuringiensis (B.t.),” by Carrie Swadener, Journal of Pesticide Reform, Fall 1994, Vol. 14, No. 3, p. 16).

Washington State's Department of Health issued a report in 1993 following an aerial application of Btk to control the gypsy moth, saying that over 250 people reported health problems and six were treated in the emergency room. The report also said that physicians could not definitively link the Btk exposure to the health problems. See “Insecticide Fact Sheet: Bacillus Thuringiensis (B.t.),” by Carrie Swadener, Journal of Pesticide Reform, Fall 1994, Vol. 14, No. 3, p. 15.

Why does Fairfax County spray insecticide to control the fall cankerworm?

In letters that Fairfax County sent in reply to the Audubon Society of Northern Virginia in 2013 and to entomologist Ashley Kennedy in 2014, two reasons are provided for the fall cankerworm insecticide spraying program:

(1) The “first problem” that the fall cankerworm spraying program is intended to address is that of a “nuisance.” The “nuisance” cited is that some County residents find the fall cankerworm spinning down from trees on a silken thread in the spring to be “particularly noticeable” plus the caterpillars “invade” outdoor living areas. Another “nuisance” as reported in The Washington Post is that some residents do not like the appearance of defoliation on their trees resulting from the fall cankerworm feeding on leaves. See “A Canker on Fairfax’s Landscape; Worms Deplete Trees, Disturb Homeowners in Mount Vernon Area” by Michael D. Shear and Peter Pae, The Washington Post, May 21, 1999, Metro, p. B01.*

(2) The “second threat” according to the County letters is that defoliation can result in harm to the trees.

Our responses to these rationales are as follows:

(1) The “spinning down” by the fall cankerworm occurs only for about one week. Caterpillars, including the fall cankerworm, are an important food source for birds and other wildlife. See above “What are caterpillars and why are they important?”. A simple annoyance does not justify the costs and risks of an aerial insecticide spraying program.

(2) Fairfax County says that the fall cankerworm poses a threat to trees even though the County does not measure whether, or to what extent, defoliation results in harm to trees or their mortality. Instead as a proxy, Fairfax County measures the presence of female moths in autumn on selected sites in the County and from that information makes estimates about whether defoliation is likely to occur. The County does not measure or describe a connection between defoliation and tree weakness or mortality. The Virginia Department of Forestry says that many variables including weather affect numbers of the fall cankerworm, but Fairfax County does not apparently measure the impact of these variables on its fall cankerworm populations. In other words, Fairfax County does not update the information that it gathers during its fall surveys of female moths to take into account the impact of intervening winter and spring weather. This omission could have been especially significant in 2014, a year in which Fairfax County experienced severe, cold winter weather and a wet spring.

Furthermore, according to Prof. Mark Ascerno, Professor Emeritus of the Department of Entomology, University of Minnesota, and Jeffrey Hahn, Entomologist:

“A mature, vigorous tree is able to withstand a single season of complete defoliation with little effect on tree health. Even two seasons of defoliation produce only a slowing of growth. However, limb dieback and loss of vigor can result if the same tree is completely defoliated for three or more consecutive years. Young, newly transplanted, or weakened trees are more susceptible to injury from defoliation. Therefore, a tree's age, size, vigor, and previous history of defoliation should be considered before choosing management tactics.”

Even Fairfax County itself does not list the fall cankerworm among the “Long Term Threats to the Health of our Forest.” Instead the most important long-term threats to trees cited by Fairfax County are urbanization and related human activities, as referenced in at least 12 of 16 items listed by the County on its Tree Action Plan webpage:http://www.fairfaxcounty.gov/dpwes/environmental/tap.htm.

In 2000, Fairfax County began its fall cankerworm insecticide spraying program following complaint calls by residents to the Fairfax County Board of Supervisors in the spring of 1999. See “A Canker on Fairfax’s Landscape; Worms Deplete Trees, Disturb Homeowners in Mount Vernon Area” by Michael D. Shear and Peter Pae, The Washington Post, May 21, 1999, Metro, p. B01.*

In 2000, Fairfax County sprayed 7,000 acres in the County with insecticide targeting the fall cankerworm. Since then, spraying by helicopter and truck has taken place in 2001 (250 acres), 2002 (300 acres), 2003 (1,400 acres), 2012 (115 acres), 2013 (2,000 acres), 2014 (2,000 acres) and 2015 (70 acres).**

The County has budgeted to spray up to 5,000 acres by helicopter and 500 acres by truck in the spring of 2017. The Fairfax County Board of Supervisors recently increased the acreage budgeted for cankerworm spraying by eleven (11) times from 500 total acres (FY 2014) to 5,500 total acres (FY 2015). This increase has continued in the FY 2016 and FY 2017 budgets.**

The Urban Forest Management Division has shared with us that spraying for fall cankerworm is unlikely to take place in the spring of 2017, although the FY 2017 Adopted Budget says “small amounts of ground treatment may be required.”

*See also Fairfax County 2008 Budget Archive, Volume 3 (Entire Volume), Lines of Business, p. 33: “In 1999, large infestations of the fall cankerworm appeared in the Mount Vernon and Lee Districts prompting the Board of Supervisors to add fall cankerworm to the list of insects that the program can control.”

Why should Fairfax County end the fall cankerworm insecticide spraying program?

Our twelve-member coalition believes that Fairfax County should end its fall cankerworm insecticide spraying program immediately for these reasons:

1. Controlling a so-called “nuisance” that poses no threat to human health or safety is not a sufficient justification for an aerial insecticide spraying program.

2. The potential harm to trees and forests posed by the native fall cankerworm caterpillar is modest, and the program does not take into account the ecological benefits provided by butterflies and moths.

3. Focusing on native tree diversity, restoration and preservation of natural spaces, and proven threats to trees such as exotic, invasive vines would be a more productive use of valuable resources.

4. While Btk is considered to be safer than many synthetic pesticides, it has downsides, including:

The commercial application of Btk sprayed by Fairfax County is comprised of 13% Btk and 87% “other” ingredients that are not publicly disclosed; these ingredients could be noxious to people (see “What is Btk?” and “What is Foray 48B?”).

Insects can develop resistance to the insecticide Btk if it is overused;* we believe that Btk should be reserved for situations in which its use is justified.

Btk is subject to the risk of “drift” outside the treatment areas; this risk puts neighboring areas potentially in the path of the insecticide spray.**

6. Leaving the fall cankerworm caterpillar alone is a sound solution, given its “native” status and its benefits, especially as a food source for other birds and other wildlife.

* For example, it has been reported that 5 of 13 major crop pests have evolved resistance to Bacillus thuringiensis in genetically engineered corn and cotton crops. Bloomberg, June 10, 2013, by Jack Kaskey.

** Various studies have shown the potential for drift of the insecticide Btk:

More than 3,000 metres [almost 2 miles] downwind in an aerial application***

“Significant” drift found up to 1,000 metres [more than ½ mile] outside the spray area****

Btk insecticide can be found in higher concentrations inside than outside by 5 hours after an aerial spraying program****

installing feeding stations or chickadee boxes to provide food and shelter for chickadees; Carolina chickadees are voracious eaters of insects, eating eggs in the winter and caterpillars in the spring (See “How can I help chickadees?”)

Carolina chickadees are voracious eaters of insects, eating eggs in the winter and caterpillars in the spring. The National Audubon Society has information on how to help chickadees by installing feeding stations and chickadee boxes:http://birds.audubon.org/species/carchi

In addition, we have some tips:

ensure the entry hole in the chickadee box is exactly 1-1/8 inches in diameter as recommended by the National Audubon Society (a larger hole for example would permit house sparrows to enter);

do not provide a perch (chickadees don’t need a perch, but other birds might use it to harass the chickadees); and

How do I band my trees to reduce the number of fall cankerworm caterpillars?

If you wish to reduce leaf damage to your trees from the fall cankerworm caterpillar, you can band your trees in autumn with a sticky glue that prevents the wingless female moths from climbing trees to lay eggs. Tree banding kits can be found at some hardware stores and online. Here is a link to one product: http://www.leevalley.com/us/garden/page.aspx?c=&cat=2,51555&p=10253

One tip is that you may need to wrap not only the tree you are trying to protect but also neighboring trees as the caterpillars, after they emerge in spring, can change trees when they spin downward towards the ground on their silken threads.

How would having a diversity of native trees help reduce the fall cankerworm?

A study recently published by North Carolina State University* looked into why fall cankerworm populations do more damage to trees in urban than in more natural or wild areas. Plant diversity plays a significant role in the difference between urban environments, which have an understory consisting only of a few shrubs, and natural areas, which are more complex with greater plant diversity. The author of the study concluded that “[t]he take-home message is that we need to take steps to make urban environments more like natural environments in terms of plant diversity.”**

Forest ecologist Suzanne Simard has spoken recently about the how a diversity of trees are important for a healthy forest, noting that forest trees are connected underground by fungal threads that allow them to transfer carbon, water and even threat warnings. See her TED Talk here: https://www.ted.com/talks/suzanne_simard_how_trees_talk_to_each_other.

If you are a resident of Fairfax County or Prince William County, urge your County Supervisors to end the spraying. You can email them using our guide for Fairfax County and Prince William County.

If your property is in a spray area, opt out of the program. Encourage your neighbors, neighborhood parks and others to opt out too. Fairfax County provides property owners with an opportunity to opt out in the spring before spraying occurs.

The Audubon Society of Northern Virginia began its formal opposition to the fall cankerworm spraying program in the spring of 2013 (see Connection Newspaper Article.) On January 20, Audubon delivered 865 signatures to our petition to the Fairfax County Board of Supervisors and the Prince William Board of County Supervisors. Audubon asked the supervisors again to terminate the fall cankerworm insecticide spraying program citing our petition and other community appeals. You can read our letter to Fairfax County here.

Also, a number of individuals and organizations, some a part of our coalition, have made important statements about the fall cankerworm spraying program. Just a few examples are below:

In this story, Should Fairfax Spray For Cankerworms? Butterfly Fans Say "No", Michael Pope interviewed Cathy Ledec, President of the Friends of Huntley Meadows Park, for WAMU.

The Friends of Huntley Meadows Park delivered written testimony for a February 17, 2015 Fairfax County Board of Supervisors meeting, canceled due to snow, including testimony from Cathy Ledec, President, public comments from George C. Ledec, Ph.D and David G. Furth, Ph.D (Entomologist), and an analysis by C. Ledec of the 1968 Bull Run fall cankerworm caterpillar project.

Katherine Wychulis, Audubon volunteer and Member of the Board of Directors of the Friends of Dyke Marsh, made a video presentation to the Fairfax County Environmental Quality Advisory Council on Jan. 11. 2017 opposing the fall cankerworm spraying program: https://vimeo.com/198235112